集团网站建设工作方案,网件路由器做网站,广西建设厅官网站首页,佛山专业做网站公司哪家好对象状态影响对象行为#xff1a; 对象拥有不同的状态#xff0c;往往会行使不同的行为... 动机#xff1a; 在软件构建过程中#xff0c;某些对象的状态如果改变以及其行为也会随之而发生变化#xff0c;比如文档处于只读状态#xff0c;其支…对象状态影响对象行为 对象拥有不同的状态往往会行使不同的行为... 动机 在软件构建过程中某些对象的状态如果改变以及其行为也会随之而发生变化比如文档处于只读状态其支持的行为和读写状态支持的行为就可能完全不同。 如何在运行时根据对象的状态来透明更改对象的行为而不会为对象操作和状态转化之间引入紧耦合意图 允许一个对象在其内部状态改变时改变它的行为。从而使对象看起来似乎修改了其行为。 ------《设计模式》GOF结构图 适用性 1.一个对象的行为取决于它的状态并且它必须在运行时刻根据状态改变它的行为。 2.一个操作中含有庞大的多分支的等条件语句且这些分支依赖于该对象的状态。这个状态通常用一个或多个枚举常量表示。通常有多个操作包含这一相同的条件结构。State模式将每一个分支放入一个独立的类中。这使得你可根据对象自身的情况将对象的状态作为一个对象这一对象可以不依赖于其他对象而独立变化。代码实现 class MainApp { static void Main() { // Open a new account Account account new Account(Jim Johnson); // Apply financial transactions account.Deposit(500.0); account.Deposit(300.0); account.Deposit(550.0); account.PayInterest(); account.Withdraw(2000.00); account.Withdraw(1100.00); // Wait for user Console.Read(); } } // State abstract class State { protected Account account; protected double balance; protected double interest; protected double lowerLimit; protected double upperLimit; // Properties public Account Account { get{ return account; } set{ account value; } } public double Balance { get{ return balance; } set{ balance value; } } public abstract void Deposit(double amount); public abstract void Withdraw(double amount); public abstract void PayInterest(); } // ConcreteState // Account is overdrawn class RedState : State { double serviceFee; // Constructor public RedState(State state) { this.balance state.Balance; this.account state.Account; Initialize(); } private void Initialize() { // Should come from a datasource interest 0.0; lowerLimit -100.0; upperLimit 0.0; serviceFee 15.00; } public override void Deposit(double amount) { balance amount; StateChangeCheck(); } public override void Withdraw(double amount) { amount amount - serviceFee; Console.WriteLine(No funds available for withdrawal!); } public override void PayInterest() { // No interest is paid } private void StateChangeCheck() { if (balance upperLimit) { account.State new SilverState(this); } } } // ConcreteState // Silver is non-interest bearing state class SilverState : State { // Overloaded constructors public SilverState(State state) : this( state.Balance, state.Account) { } public SilverState(double balance, Account account) { this.balance balance; this.account account; Initialize(); } private void Initialize() { // Should come from a datasource interest 0.0; lowerLimit 0.0; upperLimit 1000.0; } public override void Deposit(double amount) { balance amount; StateChangeCheck(); } public override void Withdraw(double amount) { balance - amount; StateChangeCheck(); } public override void PayInterest() { balance interest * balance; StateChangeCheck(); } private void StateChangeCheck() { if (balance lowerLimit) { account.State new RedState(this); } else if (balance upperLimit) { account.State new GoldState(this); } } } // ConcreteState // Interest bearing state class GoldState : State { // Overloaded constructors public GoldState(State state) : this(state.Balance,state.Account) { } public GoldState(double balance, Account account) { this.balance balance; this.account account; Initialize(); } private void Initialize() { // Should come from a database interest 0.05; lowerLimit 1000.0; upperLimit 10000000.0; } public override void Deposit(double amount) { balance amount; StateChangeCheck(); } public override void Withdraw(double amount) { balance - amount; StateChangeCheck(); } public override void PayInterest() { balance interest * balance; StateChangeCheck(); } private void StateChangeCheck() { if (balance 0.0) { account.State new RedState(this); } else if (balance lowerLimit) { account.State new SilverState(this); } } } // Context class Account { private State state; private string owner; // Constructor public Account(string owner) { // New accounts are Silver by default this.owner owner; state new SilverState(0.0, this); } // Properties public double Balance { get{ return state.Balance; } } public State State { get{ return state; } set{ state value; } } public void Deposit(double amount) { state.Deposit(amount); Console.WriteLine(Deposited {0:C} --- , amount); Console.WriteLine( Balance {0:C}, this.Balance); Console.WriteLine( Status {0}\n , this.State.GetType().Name); Console.WriteLine(); } public void Withdraw(double amount) { state.Withdraw(amount); Console.WriteLine(Withdrew {0:C} --- , amount); Console.WriteLine( Balance {0:C}, this.Balance); Console.WriteLine( Status {0}\n , this.State.GetType().Name); } public void PayInterest() { state.PayInterest(); Console.WriteLine(Interest Paid --- ); Console.WriteLine( Balance {0:C}, this.Balance); Console.WriteLine( Status {0}\n , this.State.GetType().Name); } }
结果 State模式的几个要点 1.State模式将所有一个特定状态相关的行为都放入一个State的子类对象中在对象状态切换时切换相应的对象;但同时维持State的接口这样实现了具体操作与状态转换之间的解耦。 2.为不同的状态引入不同的对象使得状态转换变得更加明确而且可以保证不会出现状态不一致的情况因为转换是原子性的----即要么彻底转换过来要么不转换。 3.如果State对象没有实例变量那么各个上下文可以共享 同一个State对象从而节省对象开销。
